Mask and vent assembly therefor

ABSTRACT

A mask ( 10 ) for use with a system for supplying breathable gas pressurized above atmospheric pressure to a human or animal&#39;s airways. The mask ( 10 ) includes a mask shell ( 12 ) which is, in use, in fluid communication with a gas supply conduit and a gas washout vent assembly ( 20 ). The gas washout vent assembly ( 20 ) includes at least one gas washout orifice ( 22 ) extending from a first side of the vent assembly ( 20 ) positioned, in use, adjacent the human or animal&#39;s face and a second side positioned, in use, adjacent the atmosphere. The cross-sectional area of the orifice ( 22 ) at the first side is larger than the cross-sectional area of the orifice ( 22 ) at the second side.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/298,845, filed Nov. 19, 2002, now allowed, which is a continuation ofU.S. application Ser. No. 09/452,558, filed Dec. 1, 1999, now U.S. Pat.No. 6,561,191, which is a continuation-in-part of U.S. application Ser.No. 09/021,541, filed Feb. 10, 1998, now U.S. Pat. No. 6,561,190, eachincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a mask and a vent assembly therefor.

The mask and vent assembly according to the invention have beendeveloped primarily for the venting of washout gas in the application ofcontinuous positive airway pressure (CPAP) treatment in conjunction witha system for supplying breathable gas pressurised above atmosphericpressure to a human or animal. Such a system is used, for example, inthe treatment of obstructive sleep apnea (OSA) and similar sleepdisordered breathing conditions. However, the invention is also suitablefor other purposes including, for example, the application of assistedventilation or respiration.

The term “mask” is herein intended to include face masks, nose masks,mouth masks, nasal pillows, appendages in the vicinity of any of thesedevices and the like.

BACKGROUND OF THE INVENTION

Treatment of OSA by CPAP flow generator systems involves the continuousdelivery of air (or other breathable gas) pressurised above atmosphericpressure to a patient's airways via a conduit and a mask.

For either the treatment of OSA or the application of assistedventilation, the pressure of the gas delivered to a patient can be at aconstant level, bi-level (ie. in synchronism with patient inspirationand expiration) or automatically adjusting in level to match therapeuticneed. Throughout this specification the reference to CPAP is intended toincorporate a reference to any one of, or combinations of, these formsof pressure delivery.

The masks used in CPAP treatment generally include a vent for washout ofthe gas to atmosphere. The vent is normally located in the mask or inthe gas delivery conduit adjacent the mask. The washout of gas throughthe vent is essential for removal of exhaled gases from the breathingcircuit to prevent carbon dioxide “re-breathing” or build-up, both ofwhich represent a health risk to the mask wearer. Adequate gas washoutis achieved by selecting a vent size and configuration that will allow aminimum safe gas flow at the lowest operating CPAP pressure, which,typically can be as low as around 4 cm H₂O for adults and 2 cm H₂O inpaediatric applications.

Prior art masks are generally comprised of a rigid plastic shell whichcovers the wearer's nose and/or mouth. A flexible or resilient rim (orcushion) is attached to the periphery of the shell which abuts and sealsagainst the wearer's face to provide a gas-tight seal around the noseand/or mouth.

A prior art washout vent utilized one or more holes or slits in therigid shell or in a rigid portion of the delivery conduit to allow thewashout gas to vent to atmosphere. In some masks, the holes or slitswere formed during the moulding process. In others, they were drilled orcut as a separate step after the shell or conduit had been moulded.

The flow of gas out the holes or slits in the shell or conduit toatmosphere creates noise and turbulence at the hole or slit outlet asthe delivered gas, and upon expiration, the patient-expired gas(including CO₂) exits. Bi-level and autosetting gas delivery regimestend to generate more noise than a constant level gas delivery regime.This is thought to be due to the extra turbulence created by the gasaccelerating and decelerating as it cycles between relatively low andrelatively high pressures. The noise adversely affects patient andbed-partner comfort.

Another prior art vent included hollow rivets or plugs manufactured fromstainless steel or other rigid materials attached to openings in therigid shell. The outer edges of the rivets were rounded to help reducenoise. However, this approach was expensive, required an extraproduction step and did not prove effective in reducing noise.

Another approach to reduce noise involved the use of sintered filters atthe gas outlet of the mask shell. However, the filters were prone toblocking, especially in the presence of moisture. Accordingly, sinteredfilters were impractical for use in CPAP treatment as they were easilyblocked by the moisture from the patient's respiratory system orhumidifiers or during the necessary regular cleaning of the mask andassociated componentry.

Foam filters wrapped around the air outlets in the shell were alsoattempted. However, they also suffered from the disadvantages of beingprone to blocking, difficult to clean and requiring constantreplacement.

Remote outlet tubes have been used to distance the noise source from thepatient. However, these tubes are difficult to clean, are prone toentanglement by the patient and/or their bed partner and suffer thefurther disadvantage that a volume of exhausted gas is retained in thetube adjacent the mask.

It is an object of the present invention to substantially overcome or atleast ameliorate the prior art disadvantages and, in particular, toreduce the noise generated by gas washout through a mask.

SUMMARY OF THE INVENTION

Accordingly, the invention, in a first aspect, discloses a mask for usewith a system for supplying breathable gas pressurised above atmosphericpressure to a human or animal's airways, the mask includes a mask shellwhich is, in use, in fluid communication with a gas supply conduit; anda gas washout vent assembly, the gas washout vent assembly includes atleast one gas washout orifice extending from a first side of the ventassembly positioned, in use, adjacent the human or animal's face and asecond side positioned, in use, adjacent the atmosphere and thecross-sectional area of the orifice at the first side is larger than thecross-sectional area of the orifice at the second side.

In a second aspect, the invention discloses a vent assembly for thewashout of gas from a mask or conduit used with a system for supplyingbreathable gas pressurized above atmospheric pressure to a human oranimal, the vent assembly includes at least one gas washout orificeextending from a first side of the vent assembly placed, in use,adjacent the human or animal's face to a second side placed, in use,adjacent the atmosphere, the cross-sectional area of the orifice at thefirst side is larger than the cross-sectional area of the orifice at thesecond side.

Preferably, the orifice includes a first substantially cylindricalportion adjacent the first side, a second cylindrical portion adjacentthe second side and a tapering portion between the first and secondsubstantially cylindrical portions.

Preferably also, the second substantially cylindrical portion and thetapering portion are of approximately equal thickness in the axial,direction of the orifice and are thicker than the first substantiallycylindrical portion.

Desirably, the vent assembly includes a plurality of said orificestherethrough.

Desirably also, each of said orifices is separated from the other(s) ofsaid orifices by at least the diameter of the orifice at the secondside.

In an aspect, at least the region of the mask shell or conduitsurrounding or adjacent the vent assembly is formed of a relativelyflexible elastomeric material. In an embodiment, the entire mask isformed from the elastomeric material. In another embodiment, the ventassembly is in the form of an insert of relatively flexible elastomericmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexamples only, with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a first embodiment;

FIG. 2 is a perspective view of a second embodiment;

FIG. 3 is a perspective view of a third embodiment;

FIG. 4 is a perspective view of a fourth embodiment;

FIG. 5 is a perspective view of a fifth embodiment;

FIG. 6 is a perspective view of a sixth embodiment;

FIG. 7 is a perspective view of a seventh embodiment;

FIG. 8 is a partial cross-sectional view of the first embodiment alongthe line 8-8 of FIG. 1;

FIG. 9 is a perspective view of an eighth embodiment;

FIG. 10 is a plan view of the insert of the third embodiment;

FIG. 11 is a cross-sectional view of the third embodiment insert alongthe line 11-11 of FIG. 10; and

FIG. 12 is a partial cross-sectional view of the third embodiment insertalong the line 12-12 of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring firstly to FIG. 1, there is shown a mask 10 for use with asystem (not shown) for supplying breathable gas pressurised aboveatmospheric pressure to a human or animal's airways. The mask includes arigid plastics shell 12 having an inlet tube 14 for connection to asupply conduit to communicate breathable gas from a flow generator (notshown) to the nasal passages of the mask wearer. The mask shell 12 alsoincludes a flexible sealing membrane 16 which is used to provide a gastight seal between the face of the wearer and the interior of the shell12. The shell 12 also includes lugs 18 for connecting the mask 10 to ahead strap (not shown) to retain the mask in place.

The mask includes a Silastic™ insert 20 through which is provided anorifice 22 for gas washout. As best shown in FIG. 8, the insert 20 has arecess or groove 24 around its periphery. A correspondingly sizedopening 26 bounded by a rim 28 is provided in the shell 12 to enable theinsert 20 to be retained in place in the fashion of a grommet. Theopening 26 can be moulded in the shell 12 or drilled or punched as apost-moulding step. The flexibility of the Silastic™ allows the insert20 to be initially squeezed through the opening 26 before resilientlyexpanding to the configuration shown in FIG. 8 and engaging the rim 28.

As seen in FIG. 8, orifice 22 has a cross-sectional contour from a faceside of the orifice to an atmosphere side of the orifice. In FIG. 8, thecontour is shown as being symmetrical between the face side of theorifice and the atmosphere side of the orifice with a central portion ofthe orifice contour being of constant diameter. After the insert 20 ispositioned in opening 26 of mask shell 12, the contour remainssubstantially constant in size as gas is passed therethrough.

FIGS. 2 to 7 show further embodiments in which corresponding referencenumerals are used to indicate like features. In all these embodimentsthe insert 20 has an external groove or recess 24 which engages the rim28 of a corresponding shaped opening 26 in the mask shell 12 to retainthe insert 20 in place.

In the embodiment shown in FIGS. 2 to 5 and 7 the insert 20 includesmore than one orifice 22. In the embodiment shown in FIG. 6, two inserts20 are provided in the shell 12.

In the embodiment shown in FIG. 9, the insert 20 is provided in a gassupply conduit 30.

FIGS. 10 to 12 show the insert 20 of the third embodiment of FIG. 3. Thedimensions 32, 34, 36, 38, 40, 42 and 45 are approximately diameter 1.73mm, diameter 3.30 mm, 28.80 mm, 19.00 mm, 1.20 mm, 1.20 mm and 3.60 mmrespectively.

The side 44 of the insert 20 faces the patient's face in use and theside 46 faces atmosphere.

The mask shell 12 is manufactured from polycarbonate. Other rigidplastics materials can equally be used. The insert 20 can bemanufactured from an elastomer sold as Silastic™ (produced by the DowCorning Corporation) or a thermoplastic elastomer sold as Santoprene™(produced by Monsanto). Other flexible elastomeric materials can be usedalso.

The mask 10 produces less noise than an identical mask having a similarsized and shaped orifice(s) formed directly in the mask shell 12 insteadof formed in the flexible insert 20. It is thought that the noisereduction occurs due to the flexible insert 20 damping vibrations causedby air passage through the orifice(s) 22 which produce vibrations orsimilar in the mask shell 12.

A prototype of the embodiment of the invention shown in FIG. 3 has beentested over a range of constant and bi-level CPAP treatment pressures.For comparison purposes, an identical mask to that shown in FIG. 3 butformed entirely from polycarbonate and having six identical arcuatelyspaced holes 22 drilled directly through the mask shell was also tested.In both masks the six holes had a diameter of 1.7 mm. The results of thetest are summarised in the Tables below:

TABLE 1 Constant level gas delivery Pressure Noise levels 1 m from mask(dBA) (cm H₂O) With flexible insert Without flexible insert 4 26.8 35.210 33.4 43.1 18 39.3 49.2

TABLE 2 Bi-level gas delivery Pressure Noise levels 1 m from mask (dBA)(cm H₂O) With flexible insert Without flexible insert  5-10 30.8-38.537.2-43.0 10-15 38.6-43.7 42.9-47.9

As the results show, the mask shown in FIG. 3 produced less radiatednoise than a similar mask not including the flexible elastomeric insert20 representing a significant advantage in terms of the comfort of themask wearer and their bed partner.

In addition to the noise reduction discussed above, the masks 10possesses other advantages over those of the prior art. Firstly, theinsert 20 is very easy to install into the mask shell 12 during eitherassembly of the mask which, is often supplied in kit form, or before andafter cleaning which is regularly required and often carried out in thehome environment. Secondly, the mask shell 12 may be produced with asingle size of opening 26 and provided with a range of different inserts20 which allows the outlet size to be “tuned” to give an optimum gaswashout rate for a particular patient's treatment pressure level.

Although the invention has been described with reference to specificexamples, it will be appreciated by those skilled in the art, that theinvention may be embodied in many other forms.

We claim:
 1. A CPAP mask assembly for use with a system for supplying breathable gas pressurized above atmospheric pressure to a human or animal, the mask assembly comprising: a mask including a rigid plastics shell and an inlet tube adapted to connect to a gas supply conduit, the shell provided with a seal to contact the human or animal in use; and a vent assembly for gas washout of CO₂-laden gas from the mask or the conduit provided to the mask while reducing noise generated by gas washout, the vent assembly including an insert attachable to the mask or conduit, the insert having at least one gas washout orifice extending from an inner side of the insert oriented, in use, towards the human or animal's face to an outer side oriented, in use, towards the atmosphere, the gas washout orifice being open in use, wherein the inner side of the insert includes an inner flanged end portion that is structured to extend inside the mask or conduit and the outer side of the insert includes an outer flanged end portion that is structured to extend outside the mask or conduit, and the insert includes a plurality of said orifices, wherein a cross-sectional area of each orifice at the inner side of the insert is larger than a cross-sectional area of each orifice at the outer side of the insert, and the insert is insertable into an opening in the mask or conduit in only a single orientation which a smaller end of each orifice is positioned at the outer side of the insert.
 2. A CPAP mask assembly as claimed in claim 1, wherein said orifices are separated from each other by at least a diameter of the orifice at the outer side.
 3. A CPAP mask assembly as claimed in claim 1, wherein the cross-sectional area of each orifice at the inner side is substantially larger than the cross-sectional area of the orifice at the outer side.
 4. A CPAP mask assembly for use with a system for supplying breathable gas pressurized above atmospheric pressure to a human or animal, the CPAP mask assembly comprising: a mask adapted to be in communication with the pressurized gas in use, the mask having an inlet tube that is, in use, adapted to be in fluid communication with a gas supply conduit, said mask including a shell made from polycarbonate or another rigid plastic material, the shell being provided with a sealing membrane to provide a gas tight seal with the user in use; and a vent assembly to exhaust CO₂-laden gas from the mask while reducing noise generated by gas washout, the vent assembly comprising: at least four gas washout orifices, each said orifice having an inner side that, in use, is oriented towards the user's face, and an outer side that, in use, is oriented towards atmosphere, each said orifice being open in use at least during the inhalation and exhalation phases of the user's breathing cycle, wherein each said orifice has a substantially round cross section along its length, and a cross-sectional size or area of each orifice at the inner side is larger than a cross-sectional size or area of the orifice at the outer side, and a transition portion between the inner and outer sides of each said orifice has a cross-sectional size or area that varies along at least a portion of a length thereof, wherein the vent assembly comprises an insert attachable to the mask, and six orifices extending through the insert, and wherein the insert is insertable into an opening in the mask in only a single orientation in which a smaller end of each orifice is positioned at the outer side of the insert.
 5. A CPAP mask assembly as claimed in claim 4, wherein the length of each said orifice is greater than an inner diameter at the inner side of each said orifice.
 6. A CPAP mask assembly as claimed in claim 4, wherein said orifices are separated from each other by at least a diameter of the orifice at the outer side.
 7. A CPAP mask assembly as claimed in claim 4, wherein an axis defined within the orifice extends substantially linearly from the inner side to the outer side.
 8. A CPAP mask assembly as claimed in claim 4, wherein the shell includes a lug on each side thereof for connecting the mask to a headgear strap to retain the mask in place relative to the user in use.
 9. A CPAP mask assembly as claimed in claim 4, wherein the length of each orifice is about 3 times a thickness of the shell.
 10. A CPAP mask assembly as claimed in claim 4, wherein each said orifice has an inner diameter at the inner side that is approximately twice an outer diameter at the outer side of the orifice.
 11. The CPAP mask assembly of claim 10, wherein the length of each said orifice is about 3.60 mm, and each said orifice has an inner diameter at the inner side of about 3.30 mm, and an outer diameter at the outer side of about 1.73 mm.
 12. The CPAP mask assembly of claim 4, wherein the vent assembly includes six orifices uniformly spaced and separated.
 13. The CPAP mask assembly of claim 12, wherein the vent assembly is arranged such that orifices provided at each end of the vent assembly are aligned along a horizontal axis.
 14. The CPAP mask assembly of claim 12, wherein the vent assembly is arranged such that all the orifices are generally aligned along a horizontal axis.
 15. A CPAP mask assembly as claimed in claim 4, wherein the cross-sectional size or area of each orifice at the inner side is substantially larger than the cross-sectional size or area of the orifice at the outer side.
 16. A CPAP mask assembly for use with a system for supplying breathable gas pressurized above atmospheric pressure to a human for treatment of obstructive sleep apnea, the CPAP mask assembly comprising: a mask including a rigid plastic shell and an inlet tube adapted to connect to a gas supply conduit, the shell provided with a flexible seal to seal against the human in use, the mask comprising polycarbonate material; and a vent assembly provided to continuously exhaust CO₂-laden gas from the mask during the entire breathing cycle of the human while reducing noise generated by gas washout, the mask including only a single opening for purposes of CO₂ washout, the single opening being delineated by a rim of said polycarbonate material, the vent assembly comprising only a single insert provided to the single opening in the mask and including a plurality of gas washout orifices, wherein at least one portion of the insert includes an inner portion defining a first flange that engages an inner surface of the rim, and an outer portion defining a second flange that engages an outer surface of the rim, the first and second flanges defining a recess or groove therebetween to receive the rim of the mask, wherein a cross-sectional area of each orifice at an inner side of the insert is larger than a cross-sectional area of the orifice at an outer side of the insert, wherein the insert comprises a material that is less rigid compared to the polycarbonate material of the rim, wherein an outer end of each orifice at the outer side of the insert is positioned outward of the outer surface of the rim, wherein the insert includes a main body and the first and second flanges are provided at the perimeter of the main body, the plurality of gas washout orifices are provided in the main body and the first and second flanges are radially outward of the plurality of gas washout orifices, and wherein the insert is insertable into the single opening in only a single orientation in which a smaller end of each orifice is positioned at the outer side of the insert.
 17. A CPAP mask assembly as claimed in claim 16, wherein the material of the insert is different from the material of the rim.
 18. A CPAP mask assembly as claimed in claim 16, wherein a thickness of the vent assembly is greater than an inner diameter of each orifice.
 19. A CPAP mask assembly as claimed in claim 16, wherein each orifice includes a cross-sectional contour that remains substantially constant in size upon application of pressurized gas at a level suitable for CPAP treatment.
 20. A CPAP mask assembly as claimed in claim 16, wherein each orifice includes a cross-sectional contour that remains substantially constant in size upon application of pressurized gas less than about 18 cmH₂O.
 21. A CPAP mask assembly as claimed in claim 16, wherein each orifice includes a cross-sectional contour that remains substantially constant in size upon application of pressurized gas in the range of 4-18 cmH₂O.
 22. A CPAP mask assembly as claimed in claim 16, wherein each orifice includes a cross-sectional contour that remains substantially constant in size upon application of pressurized gas in the range of 5-15 cmH₂O.
 23. A CPAP mask assembly as claimed in claim 16, wherein a ratio of a diameter at the inner side of each orifice to a diameter at the outer side of the orifice is about 2:1.
 24. A CPAP mask assembly as claimed in claim 16, wherein the mask includes a nose mask.
 25. A CPAP mask assembly as claimed in claim 16, wherein the vent assembly includes six orifices.
 26. A CPAP mask assembly as claimed in claim 16, wherein a length of each said orifice is greater than an inner diameter at the inner side of each said orifice.
 27. A CPAP mask assembly as claimed in claim 16, wherein the shell includes a slotted lug on each side thereof for connecting the mask to a headgear strap to retain the mask in place relative to the user in use.
 28. A CPAP mask assembly as claimed in claim 16, wherein each orifice includes a transition portion between the inner and outer sides that has a cross-sectional size or area that varies or tapers along at least a portion of a length thereof.
 29. A CPAP mask assembly as claimed in claim 16, wherein each said orifice has a substantially round cross section along its length.
 30. A CPAP mask assembly as claimed in claim 16, wherein the insert includes all of the orifices.
 31. A CPAP mask assembly as claimed in claim 16, wherein the insert includes three or more gas washout orifices.
 32. A CPAP mask assembly as claimed in claim 31, wherein the insert includes four or more gas washout orifices.
 33. The CPAP mask assembly as claimed in claim 16, wherein the insert has a thickness that is greater than a surrounding thickness of the mask.
 34. A CPAP mask assembly as claimed in claim 16, wherein the first and second flanges, respectfully, extend at substantially right angles relative to a longitudinal axis of the washout orifices.
 35. A CPAP mask assembly as claimed in claim 16, wherein a thickness of the recess or groove is approximately equal to a thickness of each of the inner and outer portions.
 36. A CPAP mask assembly as claimed in claim 16, wherein the insert is sufficiently flexible to allow the insert to be squeezed through the opening after which it expands to engage the rim.
 37. A CPAP mask assembly as claimed in claim 16, wherein the shell is made of polycarbonate.
 38. A CPAP mask assembly as claimed in claim 16, wherein the cross-sectional area of each orifice at the inner side of the insert is substantially larger than the cross-sectional area of the orifice at the outer side of the insert.
 39. A CPAP mask assembly as claimed in claim 16, wherein the second flange of the insert, as seen in cross-section, includes first and second flange portions on opposing sides of the insert to receive the rim on opposing sides of the single opening, and the first and second flange portions on each side of the insert extend a substantially equal distance from the single opening.
 40. A CPAP mask assembly for use with a system for supplying breathable gas for treatment of obstructive sleep apnea, the CPAP mask assembly comprising: (a) a rigid plastic shell having an inlet tube for connection to a conduit; (b) a flexible sealing membrane attached to the rigid plastic shell, the flexible sealing membrane and the rigid plastic shell together defining a breathing chamber; and (c) a vent assembly, the vent assembly comprising: (i) an opening in the mask assembly for receiving a removable vent insert, the opening bounded by a rim; and (ii) the vent insert having more than one orifice, the vent insert having, in at least one cross-sectional view, at least one groove at its periphery, the vent insert being removably attached to the mask assembly by the engagement of the at least one groove and the rim, wherein the vent insert is structured and configured to reduce noise during gas washout, and wherein a cross-sectional area of each orifice at an inner side of the vent insert is larger than a cross-sectional area of each orifice at an outer side of the vent insert, and the vent insert is insertable into the opening in only a single orientation in which a smaller end of each orifice is positioned at the outer side of the vent insert.
 41. The CPAP mask assembly of claim 40, wherein the opening is moulded.
 42. The CPAP mask assembly of claim 41, wherein the removable vent insert is easy to install into the mask assembly, the removable vent insert is made of a material more flexible than the rigid plastic shell and inlet tube thereby allowing the vent insert to be initially squeezed through the opening before the vent insert resiliently expands to engage the rim of the opening.
 43. The CPAP mask assembly of claim 40, wherein the removable vent insert is easy to install into the mask assembly, the removable vent insert is made of a material more flexible than the rigid plastic shell and inlet tube thereby allowing the vent insert to be initially squeezed through the opening before the vent insert resiliently expands to engage the rim of the opening.
 44. The CPAP mask assembly of claim 40, wherein the removable vent insert has at least six orifices.
 45. The CPAP mask assembly of claim 40, wherein the cross-sectional area of each orifice in the removable vent insert is substantially larger on the inner side than on the outer side.
 46. A CPAP mask for use with a system for supplying breathable gas for treatment of obstructive sleep apnea, the CPAP mask, comprising: (a) a vent assembly, the vent assembly comprising: (i) an opening in the CPAP mask for receiving a removable vent insert, the opening bounded by a rim; and (ii) the vent insert having more than one orifice, the vent insert having, in at least one cross-sectional view, at least one groove at its periphery, the vent insert being removably attached to the CPAP mask by the engagement of the at least one groove and the rim, wherein the vent insert is structured and configured to reduce noise during gas washout, and wherein a cross-sectional area of each orifice at an inner side of the vent insert is larger than a cross-sectional area of each orifice at an outer side of the vent insert, and the vent insert is insertable into the opening in only a single orientation in which a smaller end of each orifice is positioned at the outer side of the vent insert.
 47. The CPAP mask of claim 46, wherein the CPAP mask is formed of a polycarbonate.
 48. The CPAP mask of claim 47, wherein the opening is moulded.
 49. The CPAP mask of claim 46, wherein the removable vent insert is easy to install into the CPAP mask, the removable vent insert is made of a material more flexible than the CPAP mask thereby allowing the vent insert to be initially squeezed through the opening before the vent insert resiliently expands to engage the rim of the opening.
 50. The CPAP mask of claim 46, wherein the removable vent insert has at least six orifices.
 51. The CPAP mask assembly of claim 46, wherein the cross-sectional area of each orifice in the removable vent insert is substantially larger on the inner side than on the outer side.
 52. A CPAP mask assembly for use with a system for supplying breathable gas for treatment of obstructive sleep apnea, the CPAP mask assembly comprising: (a) a rigid plastic shell having an inlet tube for connection to a conduit; (b) a flexible sealing membrane attached to the rigid plastic shell, the flexible sealing membrane and the rigid plastic shell together defining a breathing chamber; and (c) a vent assembly, the vent assembly comprising: a vent insert received in an opening in the CPAP mask assembly, the opening in the CPAP mask assembly bounded by a rim, and the vent insert having more than one orifice, the vent insert having, in at least one cross-sectional view, at least one groove at its periphery, the at least one groove and the rim engaged when the vent insert is attached, wherein the vent insert is structured and configured to reduce noise during gas washout, and wherein a cross-sectional area of each orifice at an inner side of the vent insert is larger than a cross-sectional area of each orifice at an outer side of the vent insert, and the vent insert is insertable into the opening in only a single orientation in which a smaller end of each orifice is positioned at the outer side of the vent insert.
 53. The CPAP mask assembly of claim 52, wherein the opening comprises a moulded opening.
 54. The CPAP mask assembly of claim 52, wherein the vent insert is constructed and arranged to allow the vent insert to be temporarily flexed to allow insertion of a flange through the opening before the vent insert returns to its unflexed position whereby the flange engages under the rim of the opening.
 55. The CPAP mask assembly of claim 54, wherein the vent insert comprises a material that is more flexible than the rigid plastics shell and inlet tube.
 56. The CPAP mask assembly of claim 52, wherein the vent insert comprises a material that is more flexible than the rigid plastic shell and inlet tube thereby allowing the vent insert to be initially squeezed through the opening before the vent insert resiliently expands to engage the rim of the opening.
 57. The CPAP mask assembly of claim 52, wherein the vent insert has at least four orifices.
 58. The CPAP mask assembly of claim 52, wherein the vent insert is provided to the shell.
 59. The CPAP mask assembly of claim 52, wherein the vent insert is constructed and arranged to allow the vent insert to be temporarily flexed to allow an edge of the rim to enter the groove, after which the vent insert returns to its unflexed position thereby securing the vent insert relative to the rim.
 60. A CPAP mask for use with a system for supplying breathable gas for treatment of obstructive sleep apnea, the CPAP mask, comprising: a vent assembly, the vent assembly comprising: a vent insert received in an opening for purposes of CO₂ washout in the CPAP mask while reducing noise generated by CO₂ washout, the opening in the CPAP mask bounded by a rim, and the vent insert having more than one orifice, the vent insert having, in at least one cross-sectional view, at least one groove at its periphery, the at least one groove and the rim engaged when the vent insert is inserted into the opening, wherein the at least one groove of the vent insert and the opening have non-circular, complementary shapes, and wherein a cross-sectional area of each orifice at an inner side of the vent insert is larger than a cross-sectional area of each orifice at an outer side of the vent insert, and the vent insert is insertable into the opening in only a single orientation in which a smaller end of each orifice is positioned at the outer side of the vent insert.
 61. The CPAP mask of claim 60, wherein the CPAP mask is formed of a polycarbonate.
 62. The CPAP mask of claim 61, wherein the opening comprises a moulded opening.
 63. The CPAP mask of claim 60, wherein the vent insert is constructed and arranged to allow the vent insert to be temporarily flexed to allow insertion of a flange through the opening before the vent insert returns to its unflexed position whereby the flange engages under the rim of the opening.
 64. The CPAP mask of claim 63, wherein the vent insert comprises a material that is more flexible than the CPAP mask.
 65. The CPAP mask of claim 60, wherein the vent insert has at least four orifices.
 66. The CPAP mask of claim 60, wherein the vent insert is constructed and arranged to allow the vent insert to be temporarily flexed to allow an edge of the rim to enter the groove, after which the vent insert returns to its unflexed position thereby securing the vent insert relative to the rim.
 67. A CPAP mask for use with a system for supplying breathable gas for treatment of obstructive sleep apnea, the CPAP mask, comprising: a vent assembly, the vent assembly comprising: a vent insert received in an opening for purposes of CO₂ washout in the CPAP mask, and the vent insert having more than one orifice, wherein the vent insert is structured and configured to reduce noise during CO₂ washout, and wherein a cross-sectional area of each orifice at an inner side of the vent insert larger than a cross-sectional area of each orifice at an outer side of the vent insert, and the vent insert is insertable into the opening in only a single orientation in which a smaller end of each orifice is positioned at the outer side of the vent insert. 